The present invention relates to an image sensing apparatus in which a plurality of pixels share a common circuit and an image sensing system using the apparatus.
Conventionally, as an image sensing apparatus using a gain cell, or an active pixel sensor (APS), there are image sensing apparatuses utilizing MOS FET, JFET, bipolar transistor.
These image sensing apparatuses amplify photo-charges generated by photodiodes, that are photoelectric conversion elements, by various methods, then output the amplified photo-charge signals as image information. Since an amplifier for amplifying photo-charge exists in each pixel, the pixel is called a gain cell or an APS.
An APS includes an amplifier and its controller in each pixel, therefore, the percentage of an area reserved for the photoelectric conversion element in a pixel (area ratio) or area where light incidents in a pixel (aperture) tends to be small. This may cause deterioration of the dynamic range, sensitivity, and the S/N ratio of an image sensing apparatus.
As described above, when an amplifier is provided in each pixel, as shown in FIG. 40, the aperture decreases. To prevent the decrease in the area or the aperture caused by the amplifier, methods of sharing an amplifier by a plurality of pixels, as disclosed in the Japanese Patent Application Laid-Open Nos. 63-100879 and 9-46596, have been proposed.
FIGS. 41 and 42 illustrate configurations shown in the above documents. Referring to FIGS. 41 and 42, reference PD1 to PD4 denote photodiodes as photoelectric conversion elements; MTX1 to MTX4 are MOS transistors for transferring photo-charges generated by the photodiodes PD1 to PD4; MRES is a MOS transistor for resetting the MOS transistors MTX1 to MTX4 and MSF and MSEL are MOS transistors configuring an amplifier (source follower). MSEL also functions as a selection switch for selecting a pixel.
However, in the Japanese Patent Application Laid-Open Nos. 63-100879 and 9-46596, no practical layout of the foregoing elements on a chip when a plurality of pixels share a single amplifier is discussed.
Further, there is no description about a layout in a case where an amplifier, shared by a plurality of pixels, is replaced by another unit.